The present invention relates in general to an apparatus for measuring and controlling forming processes and in particular to a control circuit for measuring the forces applied to a workpiece during a cyclic multi-blow forming process.
It is well known that many forming processes, such as cold heading, forging, stamping, and the like, develop forces or loads in a workpiece which can be measured by strain gauges, piezoelectric elements, or other conventional deflection sensing elements. It is often desirable to provide a system for measuring such forces in terms of electrical signals which can be conditioned, amplified, and displayed to ultimately control the forming process. The use of such measured forces results in better workpiece quality, tool protection, and machine protection.
A multi-blow forming process is a common method of operating on a workpiece. In a typical heading operation, the workpiece is inserted into a die. A heading slide carrying a first punch is moved towards the die and performs a first impact operation on the workpiece head. The heading slide is then returned to the starting position, allowing a punch holder to index a second punch into position. On the next movement on the heading slide, the second punch imparts a second impact operation on the workpiece head. A load sensor is typically attached to the tooling or tooling holder to measure the amount of force applied to the workpiece during each impact or blow and to generate electrical load signals in response thereto.
Previous attempts to separate the two load signals representing the first and second blows of the forming process utilized mechanical cam switches mounted to the machine drive unit. The action of the heading slide caused movement of the cam switches, which movement was utilized to indicate which blow was occurring. However, such a mechanical sensing device is difficult to install and maintain in proper working order. Also, since a variety of parts are typically made on any given forming machine with a resultant difference in force for each part, it is desirable to adjust the varying load signal levels for the different blows to be within the nominal operating range of the measuring instrument and display. The mechanical cam switch sensing device described above provides no means for adjusting the varying load signal levels in the multi-blow forming process.